Back-lighted signs of the type with which the present invention is concerned are frequently mounted on the roofs of taxicabs and delivery vehicles to display advertising material. A typical roof mounted sign of the aforedescribed type generally includes a pair of horizontally elongated and laterally spaced apart translucent panels mounted at opposite sides of a supporting structure and backlighted by one or more incandescent bulbs or fluorescent lamps located between the panels. An illuminated sign of the aforedescribed type is normally visible from either side of the motor vehicle upon which it is mounted. However, such a sign is generally not readily visible when the vehicle is moving toward or away from the viewer. Further, the advertising display area provided by such a sign is usually somewhat limited.
The conventional bulbs, lamps, lamp fixtures, wiring and ballast required to maintain such signs in operation are somewhat fragile and easily damaged by road vibration. Consequently, such signs generally require frequent maintenance and part replacement with resulting downtime. Advertising contracts usually provide for downtime discount penalties which result in substantial reduction in advertising revenues when signs are out of service.
In recent years the high incidence of crime including taxicab highjackings, robberies and other crimes against cab drivers has caused at least one major U.S. municipality to adopt an ordinance requiring that taxicab companies equip each cab with an external warning display device to enable the driver of a cab to discreetly signal for police assistance if a crime is being committed within the cab or if the driver should happen to observe a crime in process in the neighborhood through which the cab is traveling. The present invention is concerned with the aforesaid problems.
Accordingly, it is the general aim of the present invention to provide an improved roof mounted, backlighted sign having increased display area, as compared with conventional signs of like kind, and which affords wide angle viewing of the sign from any viewing position relative to a vehicle upon which the sign is mounted. It is a further aim of the invention to provide a roof mounted motor vehicle sign having an improved backlighting system which provides a substantially uniform edge-to-edge illumination, free of "hot spots", and which is highly resistive to damage from road shock and vibration. Yet another aim of the invention is to provide an improved roof mounted advertising sign which may also serve as a warning device to enable a taxicab driver to discreetly signal for police assistance if a crime is being committed within his or her cab.